An approach to develop set-on-demand 3D printable limestone-calcined clay-based cementitious materials using calcium nitrate

The implementation of extrusion-based 3D concrete printing (3DCP) in large-scale constructions is currently limited by concerns regarding rheology control and the sustainability of this process. To address these issues, this study presents an approach to develop limestone-calcined clay-based cementitious (LC3) materials accelerated by Ca(NO₃)₂ solution in an inline static mixer-based 3DCP setup. Using this approach, a printable mixture containing only about 275 kg/m³ of Portland cement was formulated that can exhibit a good buildability performance and a 28-day compressive strength of over 30 MPa. Additionally, the effects of adding Ca(NO₃)₂ solution on the initial setting time, structural build-up, inline buildability, early-age hydration, and compressive strength of LC3 materials were investigated and discussed. Results show that the addition of Ca(NO₃)₂ solution improved the buildability and accelerated initial setting as well as the structuration due to the promoted ettringite precipitation and C–S–H nucleation. Furthermore, compressive strength at 7 and 28 days was improved through increasing the Ca(NO₃)₂ dosage, which can be attributed to the formation of NO₃-AFm and the increase in the amount of C–S–H gels.